Figure 1.

Neuropathic pain models involving peripheral nerve injury in the rat. (A) In chronic constriction injury (Bennett et al, 26), four chronic gut ligatures are placed around the distal sciatic nerve. They tighten and create inflammation with time, and additionally cause ischemia and axonal discontinuity. (B) The spinal nerve ligation model (Kim et al, 33) is produced by ligating and sectioning the fifth lumbar (L5) and L6 spinal nerves, so that the sciatic nerve is supplied only by the neurons of L4. This allows anatomic segregation of the axotomized (L5) and intact (L4) elements. Contributions to abnormal pain may arise from the axotomized neurons (a), or from degeneration of distal segments (b) that initiates inflammation and irritation of intact fibers (c).